The present invention relates to a sputtering target for a magnetic recording film for use in the deposition of a magnetic thin film of a magnetic recording medium, and particularly of a magnetic recording layer of a hard disk adopting the perpendicular magnetic recording system, and to a sputtering target capable of inhibiting the formation of cristobalites that cause the generation of particles during sputtering, and shortening the time required from the start of sputtering to deposition and the time is hereinafter referred to as the “burn-in time”.
In the field of magnetic recording as represented with hard disk drives, a material based on Co, Fe or Ni as ferromagnetic metals is used as the material of the magnetic thin film which is used for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys with Co as its main component are used for the recording layer of hard disks adopting the longitudinal magnetic recording system.
Moreover, composite materials of Co—Cr—Pt-based ferromagnetic alloys with Co as its main component and nonmagnetic inorganic matter are often used for the recording layer of hard disks adopting the perpendicular magnetic recording system which was recently put into practical application.
A magnetic thin film of a magnetic recording medium such as a hard disk is often produced by sputtering a ferromagnetic material sputtering target having the foregoing materials as its components in light of its high productivity. Moreover, SiO2 is sometimes added to this kind of sputtering target for a magnetic recording film as a spacer for magnetically separating the alloy phase in the sputtered film.
As a method of manufacturing a ferromagnetic material sputtering target, the melting method or powder metallurgy may be considered. It is not necessarily appropriate to suggest which method is better since it will depend on the demanded characteristics, but a sputtering target made of ferromagnetic alloys and nonmagnetic inorganic particles used for the recording layer of hard disks adopting the perpendicular magnetic recording system is generally manufactured with powder metallurgy. This is because the inorganic particles of SiO2 or the like need to be uniformly dispersed within the alloy substrate, and this is difficult to achieve with the melting method.
For example, proposed is a method of performing mechanical alloying to an alloy powder having an alloy phase prepared by the rapid solidification method and a powder configuring the ceramic phase, causing the powder configuring the ceramic phase to be uniformly dispersed in the alloy powder, and performing hot press thereto in order to obtain a sputtering target for use in a magnetic recording medium (Patent Document 1).
The target structure in the foregoing case appears to be such that the base metal is bonded in a milt (cod fish sperm) shape and surrounded with SiO2 (ceramic) (FIG. 2 of Patent Document 1) or dispersed in a thin string shape (FIG. 3 of Patent Document 1). While it is blurred in the other diagrams, the target structure in such other diagrams is also assumed to be of the same structure. This kind of structure entails the problems described later, and it cannot be said that this kind of structure is a preferred sputtering target for a magnetic recording medium. Note that the spherical substance shown in FIG. 4 of Patent Document 1 is mechanical alloying powder, and is not a structure of the target.
Moreover, without having to use the alloy powder prepared by the rapid solidification method, it is also possible to produce a ferromagnetic material sputtering target by preparing commercially available raw material powders for the respective components configuring the target, weighing these raw material powders to achieve the intended composition, mixing the raw material powders with a known method such as a ball mill or the like, and molding and sintering the mixed powder via hot press.
There are various types of sputtering devices, but a magnetron sputtering device comprising a DC power source is broadly used in light of its high productivity for the deposition of the foregoing magnetic recording film. This sputtering method causes a positive electrode substrate and a negative electrode target to face each other, and generates an electric field by applying high voltage between the substrate and the target under an inert gas atmosphere.
Here, the sputtering method employs a fundamental principle where inert gas is ionized, plasma composed of electrons and positive ions is formed, and the positive ions in the plasma collide with the target (negative electrode) surface so as to sputter the atoms configuring the target. The discharged atoms adhere to the opposing substrate surface, wherein the film is formed. As a result of performing the sequential process described above, the material configuring the target is deposited on the substrate.
As described above, SiO2 is sometimes added to this kind of sputtering target for a magnetic recording film as a spacer for magnetically separating the alloy phase in the sputtered film. When SiO2 is added to the magnetic metal material, there is a problem in that micro cracks are generated in the target and the generation of particles during sputtering increases. Moreover, with a SiO2-doped magnetic material target, there is an additional drawback in that the burn-in time becomes longer compared to a magnetic material target that is not doped with SiO2.
While there was some debate as to whether this was due to problems related to the SiO2 itself, because the SiO2 had transformed, or problems related to the interaction with other magnetic metals or additive materials, the fundamental cause had not been determined. In most cases, the foregoing problems were considered inevitable and were quietly condoned or overlooked. However, it is necessary to maintain the characteristics of magnetic films at a high level based on current demands, and the further improvement of sputtered film characterizes is being demanded.
With conventional technologies, certain documents describe the technique of adding SiO2 to a sputtering target using a magnetic material. Patent Document 2 discloses a target including a metal phase as a matrix phase, a ceramic phase that is dispersed in the matrix phase, and an interfacial reaction phase of the metal phase and the ceramic phase, wherein the relative density is 99% or more. While SiO2 is included as an option as the ceramic phase, Patent Document 2 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Upon producing a CoCrPt—SiO2 sputtering target, Patent Document 3 proposes calcining Pt powder and SiO2 powder, mixing Cr powder and Co powder to the obtained calcined powder, and performing pressure sintering thereof. Nevertheless, Patent Document 3 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Patent Document 4 discloses a sputtering target including a metal phase containing Co, a ceramic phase having a grain size of 10 μm or less, and an interfacial reaction phase of the metal phase and the ceramic phase, wherein the ceramic phase is scattered in the metal phase, and proposes that SiO2 is included as an option as the ceramic phase. Nevertheless, Patent Document 4 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Patent Document 5 proposes a sputtering target containing non-magnetic oxide in an amount of 0.5 to 15 mol %, Cr in an amount of 4 to 20 mol %, Pt in an amount of 5 to 25 mol %, B in an amount of 0.5 to 8 mol %, and remainder being Co. While SiO2 is included as an option as the non-magnetic oxide, Patent Document 5 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Note that Patent Document 6 is also listed as a reference, but this document discloses technology of producing cristobalite particles as filler of sealants for semiconductor elements such as memories. While Patent Document 6 is technology that is unrelated to a sputtering target, it relates to SiO2 cristobalites.
Patent Document 7 relates to a carrier core material for use as a electrophotographic developer. While Patent Document 7 is technology that is unrelated to a sputtering target, it relates to the types of crystals related to SiO2. One type is SiO2 quartz crystals, and the other type is cristobalite crystals.
While Patent Document 8 is technology that is unrelated to a sputtering target, it explains that cristobalite is a material that impairs the oxidation protection function of silicon carbide.
Patent Document 9 describes a sputtering target for forming an optical recording medium protection film having a structure where patternless SiO2 is dispersed in the zinc chalcogenide base metal. Here, the transverse rupture strength of the target made of zinc chalcogenide-SiO2 and the generation of cracks during of such target are affected by the form and shape of SiO2, and Patent Document 9 discloses that when the SiO2 is patternless (amorphous), the target will not crack during sputtering, even with high-power sputtering.
While this is a suggestion in some ways, Patent Document 9 first and foremost relates to a sputtering target for forming an optical recording medium protection film using zinc chalcogenide, and it is totally unknown as to whether it can resolve the problems of a magnetic material having a different matrix material.
Moreover, Patent Document 10 describes a sputtering target for use in forming an optical recording protective film with low generation of particles. In the foregoing case, described is a target in which silicon dioxide powder is dispersed in a zinc sulfide base metal, and it is described that, as the silicon dioxide powder, used is crystalline silicon dioxide powder of quartz, cristobalite, tridymite, or the like.
Patent Document 10 indicates each of the silicon dioxide powders illustrated above in an equal manner, and fails to consider the advantages and disadvantages of the respective powders.
Patent Document 11 describes a sputtering target for a magnetic recording film with low generation of particles. In addition, paragraph [0008] describes as follows: “As the silica powder as the raw material powder, crystalline silica powder is more preferably used than amorphous silica powder. The reason for this is because crystalline silica powder is less likely to become flocculated and generate coarse particles than amorphous silica powder and, therefore, abnormal discharge is less likely to occur, and the generation of particles is low.”
In the foregoing case, the reason why crystalline silica powder is more favorable is because the flocculation property is small and coarse particles are not generated easily, but there is no other description. To begin with, the main objective of the invention of Patent Document 11 is to uniformly disperse chromium oxide at the ground boundary, and no other reference is made to silica powder.
Generally speaking, there are several types of crystalline silica powder, but there is no disclosure of specific powder raw materials.
Patent Document 12 describes a sputtering target for use in forming a magnetic recording film, and its production method. In its conventional examples and comparative examples, Patent Document 12 describes as follows: “silica pulverized powder made from commercially available synthesized quartz is used”. With the invention of Patent Document 12, the silica phase in the target has an average width, which was obtained via linear analysis, within a range of 0.5 to 5 μm, and Patent Document 12 fails to disclose the role of the quartz powder in a sputtering target, and the kind of quartz powder to be selected as the optimal quartz powder.
To begin with, since the quartz used in the comparative example of Patent Document 12 is synthesized quartz, it is not surprising that Patent Document 12 fails to specifically disclose the role of the quartz powder.